Hey, scientist! I've been out exploring nature,
and check out what I spotted this afternoon: a nest with some eggs inside! After
I was done drawing a picture of my findings in my science notebook, I
decided to collect some sticks and create my own nest. Now I'll be
able to lay eggs anytime I want! What do you mean I can't lay eggs?
I already learned that animals lay eggs as part of their reproduction stage. Well, why do some animals lay eggs? Why don't humans
lay eggs? Come on, scientist,
let's investigate! We have already learned that all animals,
including humans, share some important characteristics. They move, they eat food,
and they go through a life cycle of birth, growth, reproduction, and death. But did you
know that we group animals into categories based on certain characteristics?
When we put animals into categories, it is called animal classification. There
are five main classes that animals can be sorted into: birds, mammals,
reptiles, amphibians, and fish. So e
ven though all animals are able to
reproduce, one characteristic that is used to classify animals is how they
reproduce. Some animals, like birds, lay eggs, just like the ones we see here.
Humans, on the other hand, give live birth, which means that instead of a baby coming out
of an egg, it comes out of its mother's body. Hm, so because we aren't classified as birds,
that means humans don't lay eggs. But what classification are we? Well, to figure that
out, we have to look at other charac
teristics that humans have and match them to the different
types of animals in the animal kingdom. Let's see. Another characteristic of animals is how
they control the temperature inside their bodies. There are two different ways animals
can do this, and we call them warmblooded and coldblooded. Warmblooded animals are able to
keep the temperature inside their body the same, no matter what the temperature is outside.
Humans are warmblooded because our body temperature stays about the same,
no matter
how hot or cold the air is around us. Meanwhile, coldblooded animals have a
body temperature that changes based on the temperature in their environment. This means
that their body temperature would be lower in cold weather and higher in warm weather.
Since humans are always warmblooded and we know we're not birds, there are only two
animal classes left that we could belong to: mammals, because all mammals are warm-blooded,
and fish, because fish can be warm or coldblooded. Hm, us
ing what you know about humans, make
a prediction. Do you think we are classified as fish or mammals? Let's talk about it!
We already know that all animals breathe, but let's consider how they breathe. While many
animals use lungs to breathe air, fish do not. Do you remember the body part that fish use to help
them breathe? Gills! Since fish live underwater, they need this special body part to help
them breathe. Do humans have gills? No. So that means we must not be fish. If we aren't
fish
, then what can we categorize humans as? Mammals. That's right! Just to be sure, let's see which other characteristics
humans have in common with mammals. Mammals have special teeth they use for chewing
and breaking down their food. The front teeth are often flat to help mammals bite into food, while
the teeth next to them are pointy to cut food into smaller pieces. The teeth toward the back of the
mouth are often bigger and used for grinding up food before it is swallowed by the animal.
Do
humans have teeth like this? We sure do! Mammals also have hair or fur on their bodies. Hm, well, many humans have hair on top of their
head, but did you know we also have tiny, soft hair all over our skin? Take a closer look
at your skin, and I'll bet you'll spot some. Finally, mammals can be categorized by the mothers feeding milk to their young. When human
babies are born, they don't have teeth, and they can't eat solid food. Instead, what
are they fed? Milk or formula. That's right! So,
are humans part of the mammal classification? We sure are. Wow! Today, we discovered
that humans don't lay eggs because we belong to the fascinating animal group called
mammals. Just like elephants, bears, and cats, we are warmblooded creatures who have hair
on our bodies and breathe using our lungs. I guess I don't need this nest after all! Let's
leave it for some egg-laying creatures to use. Now that you know the characteristics that
set mammals apart from other types of animals, try to
spot them in your everyday life. You
can find mammals at the park, in a book, or even in your own home. As always,
remember, science is all around you!
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